The present disclosure relates to methods for recovering data sets using existing catalog entries.
Tiered storage techniques allow for the movement of data across different tiers of a data storage infrastructure between higher-cost, higher-performance storage devices (e.g., hard disk drives) and relatively lower-cost, lower-performance storage devices (e.g., magnetic tape drives). A tiered storage management system (or hierarchical storage management system) typically has the ability to move data dynamically between different storage devices based on predictions regarding which data will be most frequently requested or used in the future. Data that has not been requested or used within a certain period of time (e.g., after one week or month) may be archived (or migrated) to a lower-cost storage device.
Some operating systems for supporting systems that perform high-volume transaction processing, such as z/OS from IBM®, manage data by means of data sets. A data set may comprise a text or binary file that includes data, such as one or more records (e.g., medical records or insurance records) used by a program running on the system. A data set may also be used to store information needed by applications running on the system (e.g., source programs or macro libraries) or by the operating system itself (e.g., system variables).
The location of an existing data set may be determined if the data set name and a corresponding data storage volume are known. A data storage volume (or volume) may comprise a unit of a data storage device that is separately addressable and may be identified by a volume identifier (e.g., a six-character volume serial number or VOLSER). In some cases, if the data set is cataloged, then only the data set name is required in order to locate the data set. However, a cataloged data set may require that the data set have a unique name or identifier. A catalog may describe various data set attributes and provide a mapping to the storage devices or volumes on which the data set is located. In some cases, a catalog and a volume table of contents (VTOC) may reside on a direct access storage device (DASD) that is mounted during operation of the system. The VTOC may list the data sets that reside on the DASD, along with information about the location and size of each of the data sets on the DASD. The system may have a master catalog containing entries for each of the catalogs that are used on the system including pointers to the catalogs. During a system initialization, the master catalog may be read to acquire system-level data sets and to determine the location of the catalogs.